/* 
 * Underlying column groups are always opened without dump or
 * overwrite, and only the primary is opened with next_random.
 */
 const char *cfg[] = {
     cfg_arg[0], cfg_arg[1], "dump=\"\",overwrite=false", NULL, NULL
 };

michaelcahill says: The intent is to catch if the column groups somehow get out of sync – once we have figured out whether a key exists in the primary (i.e., column group 0), we expect all the other column groups to give the same result.

We should review this, it's going to be slower to configure overwrite=false, especially for LSM trees.

Perhaps we should configure overwrite=false if DIAGNOSTIC is defined?